Circuit arrangement for imitating the touch of musical instruments with percussion



United States Patent Inventors Popko Reinder Di jksterhuis, deceased,

late of Bilthoven, Netherlands, by Casper Antonius Henricus Mulkens, administrator, Eindhoven, Netherlands App1.No. 719,831 Filed April 5, 1968 Patented Dec. 1, 1970 Assignee U.S. Philips Corporation New York, New York a corporation of Delaware. lby mesne assignment Priority April 8, 1967 Netherlands No. 6,705,025

CIRCUIT ARRANGEMENT FOR IMITATING THE TOUCH OF MUSICAL INSTRUMENTS WITH PERCUSSION 5 Claims, 5 Drawing Figs.

U.S. Cl 84/l.l3, 84/ l .26 Int. Cl Gl0h 3/00, GlOh H02 [50] Field ofSearch 84/1.01,

[56] References Cited UNITED STATES PATENTS 3,247,306 4/1966 Milho 84/l.l3 3,248,470 4/1966 Markowitz ct al. 84/].13X 3,321,567 5/1967 Munch 84/113 3,435,123 3/1969 Schrecongost 84/].13X 3,453,371 7/1969 Markowitz 84/101 Primary Examiner- Eli Lieberman Assistant Examiner-Timothy Vezeau Att0rney-Frank R. Trifari ABSTRACT: A control circuit for a tone generation in a key operated electronic instrument where the motion ofa magnet attached to a key generates a voltage in an associated coil, the generated voltage charges a capacitor with a voltage proportional to the intensity with which the key is depressed. The capacitor is connected to a gate circuit controlling the tone generator only after receiving a full charge, thereby eliminating the variable transient effects pulse widths induced in the coil in response to the various speeds magnet.

PATENIEDBEBI m I 3,544,695

SHEET 1 OF 2 VF M v F I 6.3

' VENTOR.

v //v POPKO REINDER DlJKSTERHUlS,Deceosed, By CASPER ANTONIUS HENRICUS MULKENS, Administrator AGEN I m'tman on: 1 mo 3.544.695

SHEETZ 0F 2 FIGS POPKO REINDER DIJKSTERHUIS, Deceased, By CASPER ANTONIUS HENRICUS MULKENS, Administrator I AGE CIRCUIT ARRANGEMENT FOR IMITATING THE TOUCH OF MUSICAL INSTRUMENTS WITH PERCUSSION The invention relates to an electronic musical instrument in which oscillations produced by tone generators are supplied to a gate member which passes these oscillations only when a gate input voltage is impressed on it. The gate input voltage is derived from a capacitor which is charged by the touch of a key to a voltage which depends upon the intensity of the touch.

In such an instrument, it is desirable that the buildup time of a tone for different intensities of touch should be kept as constant as possible or at least should not exceed a given value with a soft touch, since otherwise the character of the instrument is lost. For example, with the normal completely mechanical piano, the buildup time never exceeds 10 milliseconds.

The term buildup time is used to signify the time in which the tone rises from to its maximum amplitude. In an elec tronic piano, this time corresponds to the time in which the capacitor is charged. In prior art electronic pianos, this time is substantially inversely proportional to the rate at whicha magnet is pushed into a coil, i.e., inversely proportional to the intensity of the touch.

In order that the buildup time may substantially constant independent of the intensity of the touch, according to the invention, the voltage of the capacitor is applied to the relevant gate member by means of a switching element after the capacitor has been fully charged.

According to an embodiment of the invention, the switching element is included in the connection lead between the capacitor and the gate member. In this'case, the switching member is open during the charging process and is closed after the charging process is ended.

In an alternative embodiment, a terminal of the capacitor is connected through a resistor to the member and the switching element is included between the gate member and the other terminal of the capacitor. In this embodiment, the switching element is closed during the charging of the capacitor and is opened after the capacitor has been charged. The switching elements may be of any arbitrary kind, for example, electromagnetic switches.

In a further embodiment of a musical instrument according to the invention, the switching element is a transistor. This has the advantage that transient phenomena are substantially completely suppressed. The transient suppression is due to the curved current-voltage characteristic curve in the starting cur rent range. The voltage is impressed more or less gradually on the gate member.

In another embodiment of a musical instrument according to the invention, the switching element is actuated by a voltage induced in a coil by the magnet coupled with the key. This has the advantage that the use of mechanical switching elements can be avoided.

The invention will now be described more fully with reference to the following FIGS., of which:

FIG. 1 shows a circuit arrangement, in which the switching member is included in the connection lead between the capacitor and the gate member;

FIG. 2 shows a circuit arrangement, in which one terminal of the capacitor is connected to the gate member through a resistor and the switching element is included between the gate member and the other terminal of the capacitor;

FIG. 3 shows the circuit arrangement of FIG. 2, in which the switching element is a transistor;

FIG. 4 shows a graph of the variation of the voltage at different points of the circuit arrangement of FIG. 3; and

FIG. 5 shows the circuit arrangement of FIG. 1, in which the switching element is a transistor.

In FIG. 1, the capacitor C is charged through a diode D by a voltage which is induced in a coil L by a magnet M which is pushed into this coil L when a key T is touched. This voltage depends upon the intensity of touch. During the charging,

the capacitor and the gate member 0 is opened so that the member 0 does not pass the oscillations from the tone generator G. As soon as the capacitor has been charged, the switch S is closed so that the capacitor voltage is immediately impressed on the base of the gate member 0, which then becomes conducting, so that the oscillations can be passed.

In FIG. 2, one terminal of the capacitor is connected through a resistor R to the member 0. The member 0 is connected through a switch S to the other terminal of the capacitor C and is closed during the charging of the capacitor so that the gate member O is nonconducting. As soon as the capacitor has been charged, the switch S is opened and the gate member 0 becomes conducting so that the oscillations of the generator G can be passed.

In FIG. 3, the capacitor C, is likewise charged through a diode D, by the voltage which is induced in the coil L when a key T is touched and a magnet M is pushed into the coil L. The voltage of the capacitor C, is impressed through a resistor R, on the base of the gate member 0 in the form of a transistor with the interposition of a diode D the function of which will be explained below. The base of the gate member 0 is connected through the diode D to a resistor R, and to the collector of transistor TR, the emitter of which is connected to the other terminal of the capacitor C,. The base of this transistor is connected to the junction of the coil L and the diode D, through a resistor R,. If a positive voltage pulse is induced in this coil L, the capacitor C, is charged through the diode D,. However as soon as the voltage ofthe junction of the diode D, and the coil L becomes positive with respect to the emitter of transistor TR, this transistor becomes conducting and the capacitor voltage is short-circuited through the resistor R, so that the gate member 0 is closed and the oscillations are not passed. When the voltage pulse approaches the zero value, the transistor TR is cut off and the short circuit of capacitor C, is eliminated so that the gate member 0 is opened, as a result of which the oscillations of the generator G can be passed.

FIG. 4 shows the voltage variation of the circuit shown in FIG. 3 of the coil L as a function of time at the capacitor and at the base of the gate member 0. The first touch begins at the instant I t,, and the charging of capacitor C, also begins at this instant. The variation of the capacitor voltage V,., is also shown. At the instant t the capacitor C, is completely charged. Since the transistor TR acting as switching element has become conducting at the instant I, after its base-emitter voltage has exceeded the threshold voltage E, the base voltage of the gate member 0 is zero so that oscillations are not yet passed. The capacitor is slowly discharged through the (comparatively large) resistor R,. As soon as the voltage of the touching pulse again approaches the zero value and falls below the threshold voltage at the instant I the transistor TR is cut off again and the capacitor voltage is entirely impressed on the gate member 0 which passes the oscillations of the generator G. The voltage variation at the base of the gate member 0 is very steep and the buildup time of the tone is .considerably shorter than the touching time of the voltage pulse in the coil L and independent of the charging time of capacitor C,. This effect is further increased due to the fact that the voltage variation of the pulse in the coil is not in the usual form of a half sine, but is asymmetrical, while the declination of the trailing edge is considerably steeper than the inclination of the leading edge, as is shown by the dot and dash line, it being assumed that the intensity of touch as a function of time is constant so that the movement of the mag net is uniformly accelerated. With a touch immediately following the first touch, as is the case with a repeated touch. after the threshold voltage E has been exceeded. the gate member 0 is closed again for the time L, so that the sound would die out. This is avoided by including a diode D between the junction of transistor TR and resistor R, and the base of the gate member 0. The base of the gate member 0 is connected through a capacitor C to the supply lead of the charging circuit. When the transistor TR is cut off, the capacitor C,

transistor TR becomes conducting, the anode of the diode D which is connected to the supply lead of the charging circuit, becomes negative with respect to the cathode of D which would result in the gate member being closed. The capacitor C is discharged through the gate member 0 and the discharge time is chosen so that for the time t the gate member 0 is not completely closed so that the tone does not decay, since the base voltage of gate member 0 no longer decreases to zero in a stepwise manner. The threshold voltage of TR is required to keep the leakage current sufficiently small in the closed state. TR is preferably a silicon transistor, because the threshold voltage of such a transistor is sufficiently high.

In FIG. 5, the switch S of FIG. 1 is replaced by a transistor TR. Between the emitter and the base of transistor TR is included a series combination of a battery B and coilL a voltage being induced in this coil and simultaneously in the coil L by the magnet M when a key is touched. Thevoltage of the battery B is chosen so that the transistor TR is cut off when the key is touched and becomes conducting again after the key has been released. p

Also in this case, the building-up time is considerably shorter than touching time of the voltage pulse induced in the coil L by the magnet M, because this buildup time is determined by the steep trailing edge of the pulse,

With these circuit arrangements, the delay between the beginning of the touch of the key and the instant at which the hammer reaches the string is imitated more satisfactorily so that the touch of the electronic piano becomes similar to that ofa conventional piano.

lclaim:

l. A key operated electronic musical instrument. comprising a tone generator, gate member means for passing the output of the tone generator in response to a control signal. pulse generator means coupled to the key for generating avoltage proportional to the speed of the key, capacitor means connected across the pulse generator means for storing the generated pulse, means for converting the charge stored on the capacitor means into a control signal, and switch means connected to the converting means for passing the control signal to the gate means in response to the trailing edge of the output pulse from the pulse generating means, whereby the output of the tone generator is passed only after the capacitor means is fully charged.

2. An electronic musical instrument as claimed in claim 1. wherein the switchmeans, the capacitor means and the converting means are connected in a loop circuit. and wherein said gate means is connected to the loop circuit.

3. An electronic musical instrument as claimed in claim 2. wherein-the converting means is a resistor, and wherein the switch means is connected directly to the capacitor and the resistor.

4. An electronic instrument as claimed in claim 2, wherein said switch means comprises a transistor having base terminal and an emitter-collector path, means for connecting the base terminal to the coil, and means for connecting the emitter-collector path in the loop circuit.

5. An electronic musical instrument as claimed in claim I, wherein the switching member usedis a transistor.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3,544,695 Dated December 1, 1970 Inventofls) POPKO REINDER DIJKSTERHUIS Deceased It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page:

Priority information, item [31] "No. 6, 705,025" should read --NO. 6, 705 Ol8.

Signed and sealed this 18th day of May 1971.

(SEAL) Attest:

EDWARD M.F'LETCHER,JR.. WILLIAM E. SCHUYLER, JR Attesting Officer Commissioner of Patents 

